The invention relates to a process for treating liquids containing pollutants using ozone-containing gas and UV radiation as well as to an apparatus for carrying out the process.
The invention is directed first and foremost towards a process for treating liquids which are charged with pollutants that are difficult to oxidize. Chlorinated hydrocarbons, for example, belong to this substance group. Many of them are not biodegradable and some even have a toxic effect on organisms.
These substances can be saturated or unsaturated, aliphatic or aromatic hydrocarbons, in which some hydrogen atoms are substituted by halogens.
They can be low-molecular substances, for example the solvent trichloroethylene, or high-molecular lignins or humic acids.
Among these are compounds, which react slowly or not at all with ozone, one of the strongest oxidizing agents.
The compounds, which can hardly be broken up and which in this form cannot be attributed to the natural ecological cycle of elements and substances on our earth, are artificially and chemically synthesized to be used, for example, as propellants, coolants, solvents, pesticides and herbicides, or they are formed as by-products in some industrial processes, such as the chlorolignins formed in chlorine bleaching processes.
They seep out of garbage dumps and poison ground water and rivers. It is imperative to look for ways to detoxify these substances.
It is generally known that UV light is absorbed by some chemical compounds between the atoms in certain organic molecules and that it therefore loosens these compounds, so that they can be oxidized, that is broken up, by radicals.
Such oxidants for energetically excited compounds can be 0H radicals. OH radicals can be formed by exposing aqueous solutions of hydrogen superoxide (H.sub.2 O.sub.2) or ozone (O.sub.3) to UV, in that the parent compounds H.sub.2 O.sub.2 and O.sub.3 also absorb UV light and split off oxygen atoms, which react with the water to form 0H radicals.
Radical reactions with H.sub.2 O.sub.2 and UV on organic compounds are generally known for water conditioning [applications] and have also been described (B. Gabel, B. Stachel and W. Thiemann, Expert Reports HWW2, pp. 37-42, 1982, "Moglichkeiten der technischen Anwendung einer Kombination von Ultraviolett-Bestrahlung und H.sub.2 O.sub.2 -Behandlung zur Desinfektion von Trinkwasser und Oxidation von Inhaltsstoffen" [Possibilities for the Technical Application of a Combination of Ultraviolet Radiation and H.sub.2 O.sub.2 Treatment for Disinfecting Drinking Water and Oxidation of Components]).
In the same way, the process combinations, UV radiation and ozone, are also described (D. B. Fletcher, Water World News, vol. 3, no. 3, 1987, UV/Ozone Process Treat Toxics and K. Brooks, R. McGinty, Chemical Week, McGraw-Hill Publication, Ground Water Treatment Know-How Comes of Age and J. D. Zeff, E. Leitis, J. Barich, Ca., U.S., Ozone in Water Treatment, Vol. 1, Proceedings, 9th Ozone World Congress, New York, 1989, Uv Oxidation Case Studies on the Removal of Toxic Organic Compounds in Ground, Waste and Leachate Waters, pp. 720-731).
The Ultrox process (Ultrox =registered trademark of the firm Ultrox International, Santa Ana, Ca, V.St.v.A.) dealt with in these works has an UV-oxidant contact system for a continuous or a discontinuous liquid flow. The UV radiators are vertically mounted in a widely varying number in several chambers, which are arranged together in series. The water flows or is stagnant in these chambers and surrounds the lamps which are protected with quartz shield tubes. Ozone or other oxidants are fed into the chambers by means of jet diffusors.
The APO process (APO=registered trademark of the firm Ionization International, Dordrecht, Holland) (J.-A. Moser, M. Sc., ozone in Water Treatment, Vol. 1, Proceedings, 9th Ozone World Congress, New York, 1989, S. 732-742, The Treatment of Chlorinated Hydrocarbons at a High Concentration Level with a Photochemical Process) produces ozone with UV light of a short wavelength and enables the ozone to act in the water phase or in the gas phase on chlorinated hydrocarbons.
The problem with the H.sub.2 O.sub.2 -UV combination processes is that they do not achieve oxidation potentials that are as high as is possible with the O.sub.3 -UV combinations.
The previously known O.sub.3 -UV combination processes work with UV immersion radiators, such as Ultrox. These have large water-layer thicknesses in the radiation chambers, which are more difficult to penetrate with UV rays than is the case with continuous-flow radiators with thinner water layers. Moreover, in the case of these chambers, the ozone is fed directly with the carrier gas, whereby the ozone solution in the water is not optimal, and the gas bubbles of the gas which is not physically dissolved likewise have a disadvantageous effect for an UV-ray utilization.
The processes of generating ozone by means of UV rays, such as the APO process, or by means of electrolytic, anodic oxidation, produce ozone only in a small concentration, which is disadvantageous for the oxidizing capacity.